Apparatus for measuring ion or electron beam width by monitoring secondary emission from a moving probe

ABSTRACT

A device for measuring and displaying selected characteristics (i.e., the intensity profile distribution, the shape and the width) of molecular and/or submolecular particle beams, such as ion or electron beams, in which the beam width may be of the order of 5 microns or less, is disclosed. The device comprises a thin wire (at least 10 mils in diameter) having a very narrow zone such as a thin groove (less than 5 microns wide) along a portion of its length. When there is relative movement between the beam and the wire so that the grooved portion of the wire is passed transversely through the beam, a secondary charged particle emission current dependent upon the beam intensity and angle of incidence with the wire surface is generated and displayed on an oscilloscope as a beam intensity profile. The width of the beam is a function of the width of that portion of the profile resulting from movement of the groove across the beam.

United States Patent Ennis, Jr. et al.

[ 51 Jan. 25, I972 [54] APPARATUS FOR MEASURING ION OR ELECTRON BEAMWIDTH BY MONITORING SECONDARY EMISSION FROM A MOVING PROBE Robert M.Ennis, .Ir., Oakridge, Tenn.; Robert G. Wilson, Canoga Park, Calif.

Hughes Aircraft Company, Culver City, Calif.

Apr. 29, 1970 Inventors:

[73] Assignee:

Filed:

App]. No.:

[56] References Cited OTHER PUBLICATIONS Okabe et al., Beam ProfleMeasurements for Electron Accelerators, Japanese Journal of AppliedPhysics, Vol. 5, No. 1, Jan, 1966, pp. 68- 73 5:444 Jouzc:

. 7 I ZZ .L

Primary Examiner--Rudolph V. Rolinec Assistant ExaminerR. J. CorcoranAttorney-W. H. MacAllister, Jr. and Allen A. Dicke, Jr.

[57] ABSTRACT A device for measuring and displaying selectedcharacteristics (i.e., the intensity profile distribution, the shape andthe width) of molecular and/or submolecular particle beams, such as ionor electron beams, in which the beam width may be of the order of 5microns or less, is disclosed. The device comprises a thin wire (atleast 10 mils in diameter) having a very narrow zone such as a thingroove (less than 5 microns wide) along a portion of its length. Whenthere is relative movement between the beam and the wire so that thegrooved portion of the wire is passed transversely through the beam, asecondary charged particle emission current dependent upon the beamintensity and angle of incidence with the wire surface is generated anddisplayed on an oscilloscope as a beam intensity profile. The width ofthe beam is a function of the width of that portion of the profileresulting from movement of the groove across the beam.

13 Claims, 5 Drawing Figures arena-M4 fist/244m! APPARATUS FOR MEASURINGION OR ELECTRON BEAM WIDTH BY MONITORING SECONDARY EMISSION FROM AMOVING PROBE This invention relates to measuring apparatus generally,and more particularly to apparatus for measuring micron-width beams ofmolecular and/or submolecular particles.

This invention relates to measuring apparatus generally, and moreparticularly to apparatus for measuring micron-width beams of molecularand/or submolecular particles.

As used throughout this specification, the term particle refers to anenergetic or energized element of matter which may be accelerated andcontrolled by means of an energy source and which produces secondarycharged particle (electron and/or ion) emission current in an electricalconductor upon the occurrence of incidence with the conductor. The termbeam refers to pluralities of such particles traversing a defined pathor volume.

Using a thin wire to measure the width of a beam of molecular orsubmolecular particles is known in the art. Typically, a wire is scannedback and forth through the beam such that the motion of the longitudinalaxis of the wire is transverse to the longitudinal axis of the beam andtransverse to the longitu-- dinal axis of the wire. When the beam isincident on the surface of the wire, a secondary charged particleemission current is created in the wire, amplified, and displayed as astanding wave on an oscilloscope. This current is proportional to theintensity of the portion of the beam incident on the wire at any giventime. Therefore, when the beam intensity profile is displayed on theoscilloscope, the width of the beam may be computed by subtracting thewire diameter from the calibrated width of the profile.

A conventional method for calibrating the oscilloscope is as follows. Aplate with precisely machined slots is positioned with the plane of theplate normal to the direction of the beam so that the slotted part ofthe plate intercepts the beam before it reaches the wire. Beam particleswill be transmitted through the slots only. The time variation of theresulting secondary emission current which represents the intensity ofthe slotted beam will provide calibration of the horizontal (time) axisof the oscilloscope because the width of the slots is known. After theoscilloscope is calibrated and the slotted plate removed, the beamintensity distribution can be continuously monitored. 7

During the scanning operation, when the leading edge of the wireintercepts the near edge of the beam, secondary charged particleemission current commences, and this current increases as the wire movesthrough the beam and greater portions of the wire intercept the beam.After the leading edge of the wire emerges from the beam, the currentdecreases as smaller portions of the wire intercept the beam. Thesecondary emission current ceases after the trailing edge of the wirehas passed the far edge of the beam. The time required for the leadingedge of the wire to move from the near edge to the far edge of the beamis indicative of the beam width, while the time required for thediameter of the wire to cross an edge of the beam (such as the far edge)is indicative of the wire diameter. When the wire is of negligiblediameter compared to the beam width, the width of the secondary emissioncurrent profile is indicative of the width of the beam. emission currentprofile is indicative of the width of the beam.

Identification of the extremities of the secondary emission currentintensity profile is aided by the fact that the secondary emissioncurrent increases with increasing angle of incidence with the wire, thegreatest increase occurring as the angle of incidence approaches 90".The angle of incidence is herein defined as the angle that thelongitudinal direction of the beam makes with the normal to the wiresurface. Because the wire usually has a circular cross section (andhence the angle of incidence of the beam particles at the edge of thewire is essentially 90), as the wire enters the beam the currentincreases from zero at a much faster rate than it would for a flat stripof wire, the angle of incidence with which would be essentially zero. Asa result, the slope of the end portions of the secondary emissioncurrent profile display is quite steep. For a discussion of thedependency of secondary emission on angle of incidence, see Physics andApplications of Secondary Electron Emission by Dr. H. Bruining, M.B.E.,Pergamon Press, 1954, pages 100-103.

As is true of all measurements, some error is involved in themeasurement of the beam width. This error is the sum of the error inmeasuring the wire diameter and the error in determining the width ofthe profile on the oscilloscope screen. The wire diameter measurementerror can be reduced to less than 1/10 percent by electron microscopemeasurements. The profile width measurement error results from theinability to read the horizontal (time) axis of the oscilloscope screenmore accurately than to the nearest millimeter. Thus, on an oscilloscopescreen in which the time axis is 10 centimeters long, the minimum errorto be expected in reading the profile width is essentially 2 millimetersin l0 centimeters, or 2 percent (both ends of the profile must bedetermined). The error in measuring the wire diameter is negligiblecompared to the error in reading the oscilloscope.

In order to ensure mechanical stability during scanning, the wirethickness, or diameter, should be at least 5 mils. How ever, when wiresof this diameter are used to measure beam widths on the order of 5microns, the resultant secondary emission current profile (which isrepresentative of the sum of the width of the beam and the diameter ofthe wire) will represent a width of about 130 microns (5 mils 125microns). Even when this profile extends over the entire time axis (l0centimeters) on the aforementioned oscilloscope screen, the error inreading the profile width will correspond to about 2.6 microns, anderror which is greater than 50 percent of the beam width.

Some particle beams are nonuniform in cross section or evengeometrically irregular. For such beams, information about the particledistribution throughout the beam, c0mmonly called the internal structureof the beam, is often desired and may be obtained by use of theaforementioned scanning wire technique. However, resolution of theparticle distribution in the beam becomes poorer as the ratio of thewire diameter to the beam width increases. When the wirediameter-to-beam width ratio exceeds about 10, serious degradation inresolution begins to occur. When the ratio reaches 1, virtually allinformation about the internal structure of the beam is lost. Thus, whenbeam measuring apparatus of the prior art is employed, if the beam widthis on the order of microns, the internal structure of the beam cannot bedetermined with any satisfactory degree of accuracy, and for a beamwidth of 5 microns, it cannot be detennined at all.

It is, therefore an object of this invention to provide improvedapparatus which can be used to measure a particle beam width on theorder of 5 microns or less.

It is, therefore, an object of this invention to provide improvedapparatus which can be used to measure a particle beam width on theorder of 5 microns or less.

It is another object of the present invention to provide apparatus whichcan be used to measure the width of particle beams more accurately andwith better resolution than is possible by prior art apparatus.

Still another object of this invention is to provide apparatus which canbe used to determine the internal structure of a particle beam of widthon the order of 5 microns or less.

In accordance with the foregoing objects, apparatus according to theinvention for indicating selected characteristics of a beam of secondaryemission current producing particles includes a movable member havingfirst and second surface regions of distinguishable secondary chargedparticle emission characteristics for incident secondary emissioncurrent producing particles traveling in a predetermined direction. Themovable member defines at least two essentially linear boundariesbetween the first and second regions. The member is moved at anessentially uniform velocity through the beam such that each of theboundaries transverses the beam in a direction essentially transverse tothe longitudinal direction of the beam and essentially transverse to thelength of the boundaries. The secondary charged particle emissioncurrent resulting from the incidence of the beam on the first and secondsurface regions of the member during movement of the member through thebeam is detected. When the detected secondary charged particle emissioncurrent is displayed as a time waveform, the width of that portion ofthe waveform resulting form impingement of the beam on the first surfaceregion is indicative of the width of the beam.

The invention is described in greater detail with reference to theaccompanying drawings, in which:

FIG. 1 is a schematic view illustrating apparatus according to theinvention;

FIG. 1 is a schematic view illustrating apparatus according to theinvention;

FIGS. 2 (a, b, and c) are perspective views of three beam scanningmembers which may be used in the apparatus of FIG. 1 according torespective embodiments of the invention; and

FIG. 3 is an intensity-versus-time representation of the secondaryemission current produced with the apparatus as the scanning membermoves through the beam.

FIG. 3 is an intensity-versus-time representation of the secondaryemission current produced with the apparatus as the scanning membermoves through the beam.

Referring now to FIG. 1, there is shown a conventional secondaryemission current producing particle beam source 10 emitting a beam 12.Scanning wire 14 is mounted on an arm 16 of a conventionalelectromechanical oscillator 18 which oscillates the wire 14 back andforth through the beam 12 at a uniform velocity. The motion of thelongitudinal axis of the wire 14 is essentially transverse to thelongitudinal direction of the beam 12 and essentially transverse to thelongitudinal axis of the wire 14. The wire 14 is electrically coupled toan output terminal 20 of the oscillator 18. Terminal 20 is electricallycoupled to an input terminal 22 of a conventional amplifier 24 whichamplifies the current generated in the wire 14. An output terminal 26 ofthe amplifier 24 is electrically coupled to an input terminal 28 of aconventional oscilloscope 30 which displays the amplitude of the currentin wire 14 as a function of time.

FIGS. 2 (a, b, and c) show alternative configurations for the beamscanning wire 14 of FIG. 1 in accordance with respective embodiments ofthe invention. The wire 14a of FIG. 2a defines a longitudinal groove 32of an approximately V- shaped cross section and whose width is at moston the order of the width of the beam 12 and preferably is considerablysmaller. For example, for a beam width on the order of microns or less,the width of the groove 32 may be 1 micron or less. The width of thewire 14 is preferably at least mils.

. The two edges 33a and 33b of the groove 32 constitute essentiallylinear boundaries between the lateral surface of the wire 14a and thesurfaces of the groove 32. The length of groove 32 is greater than thelargest diameter of beam 12 anticipated. The wire 14a is oriented sothat groove 32 faces the direction of travel of the beam particles whenthe wire 14a traverses the beam 12. The surfaces of the groove 32 aresteep, presenting a large incidence angle to the beam 12, whereas thewire lateral surface adjacent the groove 32 is essentially normal to thebeam 12. As a result, the secondary charged particle emissioncharacteristics of the surfaces of the groove 32 are distinguishablefrom those of the adjacent wire lateral surface for longitudinaltraveling particles in the beam 12.

The wire 14b of FIG. 2b has a cross section of spiral configuration andan inclined longitudinal ridge 34 extending between lateral surfaceedges 35a and 35b which constitute essentially linear boundaries betweenthe lateral surface of the wire 14b and the surface of the ridge 34. Thewidth of the ridge 34 is at most on the order of the width of the beam12 and preferably is considerably smaller. The ridge 34, like the groove32, presents a steep angle of incidence to the beam 12, and itssecondary charged particle emission characteristics are distinguishablefrom those of the wire lateral surface adjacent ridge 34 forlongitudinally traveling particles in the beam 12.

The wire 140 of FIG. 2c has a longitudinally extending strip 36 of amaterial having secondary charged particle emission characteristicsdistinguishable from those of the wire material disposed along a portionof the lateral surface of the wire 14c which is to face the direction oftravel of the beam particles. Although the strip 36 is shown raised onthe surface of the wire 14c, it may also be embedded below, or flushwith the wire surface. The width of the strip 36 is at most on the orderof the width of the beam 12 and preferably is considerably smaller. Theedges 37a and 37b of the strip 36 constitute essentially linearboundaries between the lateral surface of the wire 14c and the surfaceof the strip 36. lateral surface adjacent ridge 34 for longitudinallytraveling particles in the beam 12.

The wire 14c of FIG. 2c has a longitudinally extending strip 36 of amaterial having secondary charged particle emission characteristicsdistinguishable from those of the wire material disposed along a portionof the lateral surface of the wire 14c which is to face the direction oftravel of the beam particles. Although the strip '36 is shown raised onthe surface of the wire 14c, it may also be embedded below, or flushwith the wire surface. The width of the strip 36 is at most on the orderof the width of the beam 12 and preferably is considerably smaller. Theedges 37a and 37b of the strip 36 constitute essentially linearboundaries between the lateral surface of the wire [40 and the surfaceof the strip 36.

FIG. 3 is an idealized plot of the amplitude of the secondary emissioncurrent as a function of time as wire 14 traverses the cross section ofthe beam 12 at a uniform velocity. The curve in region 38 represents thecurrent from the time when the leading edge of the wire 14 interceptsthe near edge of the beam 12 to the time when the leading edge of thewire 14 has reached the far edge of the beam 12 and the entire crosssection of the beam is incident on the wire 14. As the number ofparticles of beam 12 intercepted by wire 14 increases, an increasingnumber of secondary charged particles are emitted from the wire, causingthe current to rise in region 38.

The curve in region 40 represents the secondaryemission current from thetime when the wire 14 first intercepts the entire cross section of thebeam 12 to the time when the leading edge of the other secondary chargedparticle emission surface region of the wire 14 (i.e., groove 32, ridge34, or strip 36) reaches the near edge of the beam 12. The currentdecreases to approximately one-fifth its peak value in region 40because, as essentially the first half of the wire 14 traverses the beam12, the angle of incidence of the beam 12 (with the normal to thesurface of the wire 14) decreases from around to approximately 0. Thecurrent follows the secondary emission variation with angle of incidencediscussed by the aforementioned Bruining text. The curve in region 42represents the secondary emission current from the time when theparticles at the near edge of the beam 12 are intercepted by the leadingedge 33a of the groove 32 (or ridge 34 or strip 36) to the time when theparticles at the far edge of beam 12 are intercepted by the trailingedge 33b of the groove 32. Since groove 32 presents a relatively largeangle of incidence to particles of beam 12, the current rises sharplyafter the beam particles are first intercepted by the groove 32. Thisportion of the curve is shown in FIG. 3 as region 420. The currentcontinues to increase as a greater portion of the beam cross section isintercepted by the groove 32. If the beam 12 is approximately circularin cross section, the current reaches an approximate peak when thecenter of the beam 12 is approximately aligned with the center of thegroove 32. The current then decreases as groove 32 continues movingacross beam 12 and a smaller portion of the beam cross section isintercepted by the groove 32, until particles at the far edge of thebeam 12 are no longer intercepted by the groove 32 (i.e., when thetrailing edge 33b of the groove 32 emerges from the beam 12). Thisportion of the curve is shown as region 42b in FIG. 3.

The curve in region 44 represents the secondary emission current fromthe time when the trailing edge 33b of the groove 32 emerges from thebeam 12 to the time the wire 14 last intercepts the entire cross sectionof the beam 12. The current increases to approximately five times itsminimum value in region 44 because the angle of incidence of the beam 12on wire 14 increases from approximately 0 to around 90 as the beam 12 isscanned by essentially the latter half of the wire 14. For a cylindricalwire 14 and a symmetrical beam cross section, the curve in region 44 isthe mirror image of the curve in region 40.

The curve in region 46 represents the secondary emission current fromthe time when the trailing edge of the wire 14 crosses the near edge ofthe beam 12 and the entire cross section of the beam 12 is last incidenton wire 14 to the time when the trailing edge of wire 14 emerges fromthe far edge of the beam. The current decreases in region 46 becausedecreasing portions of the beam cross section are intercepted by thewire 14, resulting in a decrease in the number of secondary chargedparticles emitted. The curve in region 46 is the mirror image of thecurve in region 38 when the wire 14 is cylindrical and the beam 12 issymmetrical in cross section.

If beam 12 has a cross section other than circular, the current profilewill be other than that shown by the curve in FIG. 3. For example, ifthe beam 12 were a solid figure 8" in cross section and lying on itsside so that the wire 14 traverses the lobes successively, the portionof the current profile curve in region 42 would have a peak when thecenter of the groove 32 intercepts the center of each lobe, and a valleytherebetween when it intercepts the center of the figure 8."

If the beam is solid and of uniform geometrical cross section, the widthof region 42 of the resultant current vs. time profile on the screen ofthe oscilloscope 30 represents the sum of the width of beam 12 and thewidth of groove 32. If the horizontal axis on the oscilloscope screen iscalibrated in units of dimension appropriate to the beam widths beingmeasured (e.g., microns), then the beam width may be calculated simplyby subtracting the known width of the groove 32 from the calibratedwidth of region 42 on the oscilloscope screen. If beam 12 has anirregular cross section, however, the width of region 42 may not be asaccurate a representation of the sum of the widths of the beam 12 andthe groove 32 as for a beam of regular cross section. Nevertheless, itwill still be a satisfactory approximation. will still be a satisfactoryapproximation.

An alternate way of determining the width of beam 12 is by measuring thehalf-width of the current profile in region 42 (i.e., the width of theprofile between points when the amplitude is one-half of its peak valuein region 42), and using this half-width as a direct approximateindication of the beam width (i.e., ignoring the width of the groove).Although the half-width technique does not afford as accurate ameasurement of the width of beam 12 as the method involving subtractingthe width of groove 32 from the calibrated width of region 42, it is asatisfactory approximation when the width of the groove 32 is at leastan order of magnitude less than the width of the beam 12. The width ofregion 4211 and that of region 42b each represents approximately thewidth of the groove 32. The fonner represents the current as the groove32 is becoming fully immersed in the beam 12; the latter represents thecurrent as the groove 32 emerges from the beam 12.

In order to maximize the accuracy of the determination of thecross-sectional distribution of particles in the beam, it is desirableto have as narrow a groove 32 as possible. At present, the narrowestknown groove capable of use in beam width measuring apparatus is on theorder of 100A.( microns) wide. A groove thisnarrow would giveanexgellent representation of the cross-sectional distribution of theparticles in a beam whose width is on the order of 1 micron or wider.

While the invention is particularly suited for measuring.

measurement. However, for mechanical reasons, the groove width shouldnot be greater than approximately an order of magnitude of the wirediameter. Thus, for a S-mil diameter wire, the groove should be no widerthan essentially 0.5 mil.

As previously mentioned, the shape of the current profile curve inregion 42 provides information about the cross-sectional distribution ofparticles in the beam. If this cross-sectional distribution isnonsymmetrical, more complete information may be obtained bysimultaneously scanning the beam with a pair of scanning wires such asl4 moving in quadrature with one another i.e., moving at right angles toone another) and displaying the resultant current profile curves asdiscussed above.

Although the invention has been shown and described with reference toparticular embodiments, nevertheless various changes and modificationsobvious to a person skilled in the art to which the invention pertainsare deemed to be within the spirit, scope, and contemplation of theinvention.

What is claimed is:

1. Apparatus for indicating selected characteristics of a beam ofsecondary emission current producing particles comprising:

a movable member having first and second surface regions ofdistinguishable secondary charged particle emission characteristics forincident secondary emission current producing particles traveling in apredetennined direction and defining at least two essentially linearboundaries between said first and second regions;

means coupled to said member for moving said member at an essentiallyuniform velocity through said beam such that each of said boundariestraverses said beam in a direction essentially transverse to thelongitudinal direction of said beam and essentially transverse to thelength of said boundaries; and

means coupled to said member for indicating the secondary chargedparticle emission current resulting from the incidence of said beam onsaid first and second surface re gions during the movement of saidmember through said beam.

2. The apparatus claimed in claim 1 wherein said movable member is awire at least essentially 1 cm. long.

3. The apparatus claimed in claim 1 wherein the last-named meanscomprises an oscilloscope for displaying said secondary charged particleemission current as a waveform, the portion of said waveform resultingfrom impingement of said beam on said first surface region having awidth representative of the width of said beam and said first surfaceregion.

4. The apparatus claimed in claim 1 wherein the lateral surface of saidmember has a longitudinal groove therein which defines said firstsurface region, the remainder of the lateral surface of said memberdefining said second surface region.

5. The apparatus claimed in claim 1 wherein the lateral surface of saidmember has a longitudinal ridge therein which defines said first surfaceregion, the remainder of the lateral surface of said member definingsaid second surface region.-

6. The apparatus claimed in claim 1 wherein the lateral surface of saidmember has a strip of material of secondary charged particle emissioncharacteristics distinguishable from those of said member disposedlongitudinally thereon, said strip defining said first surface regionand the exposed lateral surface of said member defining said secondsurface region.

7. The apparatus claimed in claim 1 wherein the width of said firstsurface region is at least essentially an orderof magnitude smaller thanthe width of said member.

8. ln apparatus for indicating selected characteristics of a beam ofsecondary emission current producing particles wherein a scanning memberis moved at an essentially uniform velocity through said beam in adirection essentially transverse to the longitudinal direction of saidbeam and essentially transverse to the length of said member, andwherein the secondary charged particle emission current resulting fromthe incidence of said beam on said member during the movement of saidmember through said beam is detected, the improvement comprising ascanning member having first and second surface regions ofdistinguishable secondary charged particle emission characteristics forincident secondary emission current producing particles traveling in apredetermined direction and defining at least two essentially linearboundaries between said first and second regions.

9. A scanning member according to claim 8 wherein said member is a wireat least essentially 1 cm. long.

10. A scanning member according to claim 8. wherein the lateral surfaceof said member has a longitudinal groove therein which defines saidfirst surface region, the remainder of the lateral surface of saidmember defining said second surface region.

11. A scanning member according to claim 8 wherein the lateral surfaceof said member has a longitudinal ridge therein which defines said firstsurface region, the remainder of the lateral surface of said memberdefining said second surface regron.

12. A scanning member according to claim 8 wherein the lateral surfaceof said member has a strip of material of secondary charged particleemission characteristics distinguishable from those of said memberdisposed longitudinally thereon, said strip defining said first surfaceregion, and the exposed lateral surface of said member defining saidsecond surface regron.

13. A scanning member according to claim 8 wherein the width of saidfirst surface region is at least essentially an order of magnitudesmaller than the width of said member.

In order to maximize the accuracy of the determination of thecross-sectional distribution of particles in the beam, it is desirableto have as narrow a groove 32 as possible. At present, the narrowestknown groove capable of use in beam width measuring apparatus is on theorder of I A.(l0 microns) wide. A groove this narrow would give anexcellent representation of the cross-sectional distribution of theparticles in a beam whose width is on the order of 1 micron or wider.

While the invention is particularly suited for measuring beam widths onthe order of 5 microns or less, it is also well suited for measuringbeam widths greater than 5 microns. lndeed, for a given groove width,the larger the beam the more accurate the measurement. Furthermore,wider grooves may be used for larger width beams without degradation'ofthe measurement. However, for mechanical reasons, the groove widthshould not be greater than approximately an order of magnitude of thewire diameter. Thus, for a 5-mil diameter wire, the groove should be nowider than essentially 0.5 mil.

As previously mentioned, the shape of the current profile curve inregion 42 provides information about the cross-sectional distribution ofparticles in the beam. If this cross-sectional distribution isnonsymmetrical, more complete information may be obtained bysimultaneously scanning the beam with a pair of scanning wires such as14 moving in quadrature with one another (i.e., moving at right anglesto one another) and displaying the resultant current profile curves asdiscussed above.

Although the invention has been shown and described with reference toparticular embodiments, nevertheless various changes and modificationsobvious to a person skilled in the art to which the invention pertainsare deemed to be within the spirit, scope, and contemplation of theinvention.

What is claimed is:

1. Apparatus for indicating selected characteristics of a beam ofsecondary emission current producing particles comprising:

a movable member having first and second surface regions ofdistinguishable secondary charged particle emission characteristics forincident secondary emission current producing particles traveling in apredetermined direction and defining at least two essentially linearboundaries between said first and second regions;

means coupled to said member for moving said member at an essentialluniform velocity through said beam such that each 0 said boundariestraverses said beam m a direction essentially transverse to thelongitudinal direction of said beam and essentially transverse to thelength of said boundaries; and

means coupled to said member for indicating the secondary chargedparticle emission current resulting from the incidence of said beam onsaid first and second surface regions during the movement of said memberthrough said beam.

2. The apparatus claimed in claim 1 wherein said movable member is awire at least essentially 1 cm. long.

3. The apparatus claimed in claim 1 wherein the last-named meanscomprises an oscilloscope for displaying said secondary charged particleemission current as a waveform, the portion of said waveform resultingfrom impingement of said beam on said first surface region having awidth representative of the width of said beam and said first surfaceregion.

4. The apparatus claimed in claim 1 wherein the lateral surface of saidmember has a longitudinal groove therein which defines said firstsurface region, the remainder of the lateral surface of said memberdefining said second surface region.

5. The apparatus claimed in claim 1 wherein the lateral surface of saidmember has a longitudinal ridge therein which defines said first surfaceregion, the remainder of the lateral surface of said member definingsaid second surface region.

6. The apparatus claimed in claim 1 wherein the lateral surface of saidmember has a strip of material of secondary charged particle emissioncharacteristics distinguishable from those of said member disposedlongitudinally thereon, said strip defining said first surface regionand the exposed lateral surface of said member defining said secondsurface region.

7. The apparatus claimed in claim 1 wherein the width of said firstsurface region is at least essentially an order of magnitude smallerthan the width of said member.

8. ln apparatus for indicating selected characteristics of a beam ofsecondary emission current producing particles wherein a scanning memberis moved at an essentially uniform velocity through said beam in adirection essentially transverse to the longitudinal direction of saidbeam and essentially transverse to the length of said member, andwherein the secondary charged particle emission current resulting fromthe incidence of said beam on said member during the movement of saidmember through said beam is detected, the improvement comprising ascanning member having first and second surface regions ofdistinguishable secondary charged particle emission characteristics forincident secondary emission current producing particles traveling in apredetennined direction and defining at least two essentially linearboundaries between said first and second regions.

9. A scanning member according to claim 8 wherein said member is a wireat least essentially 1 cm. long.

10. A scanning member according to claim 8 wherein the lateral surfaceof said member has a longitudinal groove therein which defines saidfirst surface region, the remainder of the lateral surface of saidmember defining said second surface region.

ll. A scanning member according to claim 8 wherein the lateral surfaceof said member has a longitudinal ridge therein which defines said firstsurface region, the remainder of the lateral surface of said memberdefining said second region.

12. A scanning member according to claim 8 wherein the lateral surfaceof said member has a strip of material of secondary charged particleemission characteristics distinguishable from those of said memberdisposed longitudinally thereon, said strip defining said first surfaceregion, and the exposed lateral surface of said member defining saidsecond surface regron.

13. A scanning member according to claim 8 wherein the width of saidfirst surface region is at least essentially an order of magnitudesmaller than the width of said member.

s s s s s 29 UNITED S'IA'IES PATENT OFFICE CERTIFICATE OF CORRECTIQNPatent No. 3 I lll Dat d January 25, 1972 Inventor(s) Robert M. Ennis,Jr. et al It: is certified that: error appears in the above-identifiedpatent and that said Letters Patent are hereby corrected as shown below:

r- Column 1, lines 7 through 9, delete "This invention articles. (page2, lines 1 through 4) (Duplication) Column 1, lines 61 and 6.2, delete"emission current of the beam. (page 4, lines 1 and 2) (Duplication)Column 2, line 32, delete "and" and substitute --an. (page 5, line 23)Column 2, lines 54 through 56, delete "It is, less." (page 6, lines 15through 17) (Duplication) Column 3, lines 14 and 15, delete "FIG. linvention; (page 7, lines 23 and 24) (Duplication) Column 3, lines 23through 25, delete "FIG. 3 beam. (page 8, lines 1 through -3)(Duplication) Column 4, 4 lines through 14, delete "The wire 14c I beam12. (page 10, lines 3 through 16') (Duplication) Column 4, line 51,after "text." begin a new paragraph. (page ll, line 15) Column 5, line42, delete "will approximation. (page l4, line 1) (Duplication) Column5, line 72, delete "5 mieros" and insert 5 microns-- (page 15, line 4)Column 7, line 28 through column 8, line 71, delete "In orde;

"member. (Page 14 line 14 through end) (Duplication) Signed and sealedthis 6th day of March 1973.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissionerof Patents

1. Apparatus for indicating selected characteristics of a beam ofsecondary emission current producing particles comprising: a movablemember having first and second surface regions of distinguishablesecondary charged particle emission characteristics for incidentsecondary emission current producing particles traveling in apredetermined direction and defining at least two essentially linearboundaries between said first and second regions; means coupled to saidmember for moving said member at an essentially uniform velocity throughsaid beam such that each of said boundaries traverses said beam in adirection essentially transverse to the longitudinal direction of saidbeam and essentially transverse to the length of said boundaries; andmeans coupled to said member for indicating the secondary chargedparticle emission current resulting from the incidence of said beam onsaid first and second surface regions during the movement of said memberthrough said beam.
 2. The apparatus claimeD in claim 1 wherein saidmovable member is a wire at least essentially 1 cm. long.
 3. Theapparatus claimed in claim 1 wherein the last-named means comprises anoscilloscope for displaying said secondary charged particle emissioncurrent as a waveform, the portion of said waveform resulting fromimpingement of said beam on said first surface region having a widthrepresentative of the width of said beam and said first surface region.4. The apparatus claimed in claim 1 wherein the lateral surface of saidmember has a longitudinal groove therein which defines said firstsurface region, the remainder of the lateral surface of said memberdefining said second surface region.
 5. The apparatus claimed in claim 1wherein the lateral surface of said member has a longitudinal ridgetherein which defines said first surface region, the remainder of thelateral surface of said member defining said second surface region. 6.The apparatus claimed in claim 1 wherein the lateral surface of saidmember has a strip of material of secondary charged particle emissioncharacteristics distinguishable from those of said member disposedlongitudinally thereon, said strip defining said first surface regionand the exposed lateral surface of said member defining said secondsurface region.
 7. The apparatus claimed in claim 1 wherein the width ofsaid first surface region is at least essentially an order of magnitudesmaller than the width of said member.
 8. In apparatus for indicatingselected characteristics of a beam of secondary emission currentproducing particles wherein a scanning member is moved at an essentiallyuniform velocity through said beam in a direction essentially transverseto the longitudinal direction of said beam and essentially transverse tothe length of said member, and wherein the secondary charged particleemission current resulting from the incidence of said beam on saidmember during the movement of said member through said beam is detected,the improvement comprising a scanning member having first and secondsurface regions of distinguishable secondary charged particle emissioncharacteristics for incident secondary emission current producingparticles traveling in a predetermined direction and defining at leasttwo essentially linear boundaries between said first and second regions.9. A scanning member according to claim 8 wherein said member is a wireat least essentially 1 cm. long.
 10. A scanning member according toclaim 8 wherein the lateral surface of said member has a longitudinalgroove therein which defines said first surface region, the remainder ofthe lateral surface of said member defining said second surface region.11. A scanning member according to claim 8 wherein the lateral surfaceof said member has a longitudinal ridge therein which defines said firstsurface region, the remainder of the lateral surface of said memberdefining said second surface region.
 12. A scanning member according toclaim 8 wherein the lateral surface of said member has a strip ofmaterial of secondary charged particle emission characteristicsdistinguishable from those of said member disposed longitudinallythereon, said strip defining said first surface region, and the exposedlateral surface of said member defining said second surface region. 13.A scanning member according to claim 8 wherein the width of said firstsurface region is at least essentially an order of magnitude smallerthan the width of said member. Although the invention has been shown anddescribed with reference to particular embodiments, nevertheless variouschanges and modifications obvious to a person skilled in the art towhich the invention pertains are deemed to be within the spirit, scope,and contemplation of the invention.